The present invention relates generally to antenna assemblies for wireless communication devices and systems, and in particular to multiple band antenna assemblies. The invention provides particular utility to multiple polarization antennas for with telecommunications devices, or other wireless devices.
There is a need for a multiple band, isolated feed antenna assembly for efficient operation over a variety of frequency ranges. A further need exists for such an antenna to be suitable for mounting within a communication device and yet have little or no operational interference from other internal components of the device. In addition, there is a need for such antennas to provide polarization diversity, useful for reducing the effects of multipath.
Existing antenna structures for wireless devices include both external and internal structures. External single or multi-band wire dipole antennas are half wave antennas operating over one or more frequency ranges. The typical gain is +2 dBi. These antennas have no front to back ratio and therefore radiate equally toward and away from the user of the wireless device without Specific Absorption Rate (SAR) reduction. LC (inductor and capacitor) traps may be used to achieve multi-band resonances. The bandwidth near the head is limited to 80 degrees nominal.
Another external antenna structure is a single or multi-band asymmetric wire dipole. This antenna is a quarter wave antenna operating over one or more frequency ranges. The typical gain is +2 dBi. There is no front to back ratio or SAR reduction. LC traps may be used to achieve multi-band resonances. An additional quarter wave conductor is needed to achieve additional resonances. The beamwidth near the head is limited to 80 degrees nominal.
Internal single or multi-band antennas include asymmetric dipole antennas. These antennas include quarter wave resonant conductor traces, which may be located on a planar, printed circuit board. These antennas operate over one or more frequency ranges with a typical gain of +1 to +2 dBi, and have a slight front to back ratio and reduced SAR. These antenna structures may have one or more feedpoints, and require a second conductor for a second band resonance.
Another internal antenna structure is a single or multi-band planar inverted F antenna, or PIFA. These are planar conductors that may be formed by metallized plastics. PIFA operate over a second conductor or a ground plane. The typical gain for such antennas is +1.5 dBi. The front to back ratio and SAR values are dependent of frequency.
Yet other known antenna structures include quadrifilar helix and turnstile antenna structures providing circular polarization.
A multiple band antenna for internal installation in wireless communications devices is described. The antenna includes a plurality of feed points, one each for an associated transmission and reception band. Importantly, the antenna provides enhanced isolation between the plurality of feed points. Additionally, the antenna assembly may be incorporated within such devices with minimal operational interference.
Another object of the invention is to provide an antenna integrated upon a transceiver board for ease and economy of manufacture. The antenna assembly is of a compact size suitable for mounting directly on the printed wiring board of a wireless communications device. The antenna is preferably positioned at an upper rear side of the device.
The antenna assembly of the present invention also preferably provides a dual band antenna for wireless communications devices having separated feeds for each band and isolation between feed points in the range of 10-24 dB.
Other objects and advantages include the provision of: a dual band antenna that exhibits elliptical polarization in at least one of the bands; a relatively high bandwidth; and amenability to efficient mass production processes.
In one embodiment, the antenna assembly may be disposed away from the ground plane of an associated wireless communications device and coupled via a pair of signal transmission lines such as RF coax lines, microstrip transmission lines, coplanar wave guides, or other known signal transmission approaches as appreciated by those skilled in the arts.